This invention relates generally to air conditioning systems employed in automobiles, trucks, tractors, motor homes, and other vehicles and more particularly to manually controlled air conditioning systems that do not utilize an automatic temperature control, commonly referred to as a climate control system.
It has been established that a considerable amount of fuel is wasted in vehicles that are not equipped with a climate control system because the air conditioner compressor is engaged 100% of the time. The temperature inside the vehicle can only be increased by manually adjusting the temperature lever to a higher setting, which causes warm air from the heater to be mixed with cold air from the air conditioner, while the air conditioner compressor is engaged full time. Testing has shown that the heat sink capability or thermal time constant of the vehicle air ducts results in circulation of cool inside air for several minutes after the air conditioner compressor has been turned off before the inside air temperature has risen to the point at which operation of the compressor is again required. Since operation of the air conditioner compressor represents a substantial incremental load on the engine of a small vehicle, a significant fuel saving can be realized when the compressor is not engaged.
Several prior art references are directed to timing control of manually operated vehicle air conditioning systems. U.S. Pat. No. 4,202,613 to Schockley is directed to an air conditioner control system that serves to prevent engagement of the compressor for a given fixed period of time immediately after starting the vehicle engine and during periods of vehicle acceleration. U.S. Pat. No. 4,274,265 to Okumura is directed to an apparatus that enables operation of a vehicle cooling and heating system at a preset time and only when the temperature inside the vehicle is outside a suitable range, as compared with a preset temperature. U.S. Pat. No. 4,424,682 to Miska et al. is directed to a vehicle air conditioning compressor control system that prevents cycling of the compressor when the vehicle speed falls below a predetermined limit. U.S. Pat. No. 4,480,443 to Nishi et al. is directed to an automotive refrigeration system in which the displacement of a variable displacement compressor is controlled to be in a minimum position at the time the compressor is engaged to thereby prevent frosting or icing on the fins of the evaporator. U.S. Pat. No. 4,481,784 to Elmslie is directed to an automotive air conditioner control system in which the normal cycling of the compressor is inhibited during engine idle conditions so that the compressor remains either continuously on or continuously off, U.S. Pat. No. 4,733,540 to Sakurai is directed to a control system for a vehicular air conditioner compressor that operates to disengage the compressor for a period of time following abrupt vehicle acceleration or following detection of a fuel system overheat condition. U.S. Pat. No. 4,909,043 to Masauji et al. is directed to an air conditioning control system for automotive vehicles in which a variable capacity compressor is controlled to perform cool-down control with the compressor set to full capacity, irrespective of the cooling degree of the evaporator, to thereby prevent freeze-up of the evaporator,
It is therefore the principal object of the present invention to provide an air conditioner compressor controller, for use with less expensive vehicle air conditioner systems that do not employ climate control, for repeatedly cycling the compressor on and off in a predetermined, but adjustable, manner to thereby effect significant fuel savings.
This and other objects are accomplished in accordance with the illustrated preferred embodiment of the present invention by employing an adjustable timer to repeatedly cycle the compressor on and off. The timer is adjustable by the driver to compensate for changes in outside air temperature and the effect on the inside temperature of the vehicle produced by the sun. A thermostat may be employed in combination with the adjustable timer to provide overriding adjustable temperature control to prevent the timer from engaging the compressor until the temperature inside the vehicle rises to a predetermined level. The adjustable timer of the present invention may be very simply added to existing automobile air conditioning systems.